Finishing process for metallic surfaces



3,543,452 FINISHING PROCESS FOR METALLIC SURFACES Charles J. Guenther,Mankato, Minn., assignor to International Business Machines Corporation,Armonk, N.Y-, a corporation of New York No Drawing. Filed Mar. 1, 1968,Ser. No. 709,790 Int. Cl. B24b 1/00 US. Cl. 51313 9 Claims ABSTRACT OFTHE DISCLOSURE A method for improving surface smoothness of a surfacehaving particles of a hard, wear resistant substance embedded in a metalmatrix involving a minimum of matrix particle removal. Parts to befinished are tumbled or vibrated in an aggressive media in the presenceof a liquid containing a wetting agent.

BACKGROUND OF THE INVENTION This invention pertains to surface finishingand more particularly, to enhancing the surface smoothness of partshaving a surface layer of hard abrasion resistant particles embedded ina metal matrix.

When a machine part in use is subject to contact with another articlesuch as a business machine subjected to contact with a moving recordmedium, it is required that a Wear resistant surface be provided atlocations of contact. It is necessary that the surface presented isabrasion resistant and further presents a smooth enough surface to avoiddamage to the medium being handled. One means of providing a wearresistant surface is to plate a metal part with a metal matrix materialwhich carries particles of hard wear resistant material. A common matrixusing this procedure is a nickel matrix bearing silicon carbideparticles which is electroplated on the part. While this processing ofthe part provides a wear resistant surface that protects the machine ofwhich the parts are a portion, the contact surface so provided may besufficiently irregular to damage the record medium with which it mustcome in contact.

To overcome this disability it is necessary that the smoothness of thefinish be improved. This must however be accomplished withoutcompromising the surfacing material when the latter has been applied tothe part as by electroplating and comprises only a thin layer. Grindingpolishing or other surface treatment that improves the surface finish byremoval of material must be accomplished with great care to assure thatthe surfacing layer is not wholly removed or compromised in itseffectiveness by removing the abrasion resisting particles from thesurface of the matrix. There is further a tendency for a grinding orpolishing device to push particles along the matrix surface to gall anddeface the surface rather than shear the particle to a uniform height toimprove the sur face regularity.

Parts which are to have the surface improved might be tumbled with metalshot, but in such a process damage is likely to occur to parts as aresult of the Weight of the media even if liquid is utilized to overcomea portion of the weight disability through floatation. In additon, itwill be necessary to have a media which was sufficiently hard to beeffective in treating the surface presenting principally silicon carbideparticle surfaces. Heavy shot would tend to chip the metal coating ordent the coating, impairing the bond between the surface material andsubstrate and rendering the surface material susceptible to chipping.

nited States Patent Patented Dec. 1, 1970 In the process of thisinvention the parts are loaded into a tumbling barrel or vibratorycontainer in intimate contact with an aggressive media of preformedceramic bodies. Also included is a liquid including a wetting agent andwhere it is desirable to accelerate the action, a light grindingcompound is utilized. When tumbled or vibrated in the presence of suchmedia, a surface finish improvement based on the arithmetical averagestandard (AA) can be achieved in the realm of a reduction from theapproximate AA of the part surface as plated to an 8AA, far surpassingthe required 32AA specified in many environments. Of equal importance isthe fact that this improved surface condition is attained withoutsignificant removal of wear resistant material. In many instances it ishardly possible to identify any removal of the particles of wearresistant material. Although an aggressive particle is utilized in thepreformed media, the observed result of the process is a peening actionwherein the wear resistant particles such as silicon carbide are kneadedinto a metal matrix, such as nickel with negligible particle removal. Asa consequence, the density of such particles at the surface is at leastas great subsequent to processing as it was prior to processing. It willaccordingly be appreciated that the method of this invention hasparticular utility when used on parts having a relatively thinelectroplated coating of a metal matrix containing Wear resistantparticles.

It is an object of this invention to provide an improved process forenhancing the surface smoothness of part surfaces formed of discreteadditive particles of wear resistant material in a metal matrix.

It is a further object of the method of this invention to improve thesurface smoothness of a surface formed of particles of wear resistantmaterial in a metal matrix without reducing the density of wearresistant material particles at the matrix surface.

It is also an object of this invention to provide a method forenhancement of the surface smoothness of an electroplated metal matrixcontaining wear resistant ma terial particles which does not impair thebond between the electroplated surface material and the substratematerial.

The foregoing and other objects, features and advantages ofthe'invention will be apparent from the following more particulardescription.

DETAILED DESCRIPTION When a tumbling operation is utilized, the barrelis loaded to the operating level with preformed ceramic media. Normallya single size media body is utilized with the size and shape determinedby the part configuration. The media body must be of a size and shape toreach corner or short redius portions of part surfaces to be treated,but must not be of a size which might lodge in an apertured or notchedportion of the part or parts being processed. To simplify thisdetermination and also separation at the end of the process it is normalpractice to process parts of a single design in a given operation. Wateris thereafter added to substantially the level of the media and awetting agent or a combined wetting agent and compound added in anamount of three ounces per cubic foot of media. Following tumbling ofthe media sufficiently to assure a satisfactory mixture of the componentportions thereof, the parts are added to the media mass in a volumetricratio of one volume of parts to four volumes of media. The time of thetumbling operation varies depending upon the initial surface condition,the final surface condition required and whether a grinding compound isused, but normally a three to five hour cycle time is required.

When it is desirable or necessary to restore the color and remove oxidesor remove a residue build-up on processed parts, a secondary tumblingprocess may be utilized using preformed media and water as above and oneounce of detergent for each cubic foot of media. A norm one hour cycletime is utilized when this secondary operation is used.

In the tumbling process the entire mass of media and parts iscontinuously revolved causing media elements to fall back against thepart surfaces during one portion of the cycle. Where parts of a moredelicate nature are being processed, a vibratory process often provesmore satisfactory.

In the vibratory process, the vibratory tub is loaded to the operatinglevel with preformed ceramic, abrasive media selected in accordance withpart requirements as in the tumbling process and a quantity of wateradded sufficient only to maintain media and part surfaces moist. A lowfoaming wetting agent or a low foaming grinding compound including afinely ground abrasive and low foaming detergent is added in an amountof about three ounces per cubic foot of media. Following thoroughadmixture of the media within the vibratory tub, parts to be processedare added in the ratio of one volume of parts to four volumes of media.The cycle time varies in accordance with the initial and terminalsurface conditions and whether a compound is used varying from one tofive hours.

Following the primary cycle the parts are rinsed and a secondary processmay be used to remove residue and restore the color by removal of oxidesby vibrating media and parts using one ounce of low foaming detergentThe part to be processed is aluminum coated with a nickel matrixcarrying silicon carbide particles. The part is not delicate, having aminimum thickness of one-fourth inch, with no surfaces requiring closealignment and therefore may be tumbled. A preformed triangular mediainch on each side and 7 inch thick of aluminum oxide is selected sincethe part includes a 0.219 inch diameter aperture in which smaller sizemedia particles might lodge.

A tumbling barrel is loaded with the above media to the operating level.Water is added to the operating level, and a compound containing finelyground silicon carbide and detergent is added in the amount of threeounces per cubic foot of media. The media is tumbled sufficiently toeffect mixing and the parts added. The cycle time is four hoursfollowing which the processed parts are separated from the media byscreening.

The part surface as plated has a surface character in a nominal range of90110AA with a mean value of IOOAA while a final surface condition isspecified as not in excess of 32 AA. After the tumbling process asspecified the surface of the coating of silicon carbide and nickel hasattained a finish in the range of 2530AA.

EXAMPLE II The part to be processes is formed of aluminum with anelectroplated coating of nickel carrying particles of silicon carbide.The part has a half inch diameter aperture, a 0.63 inch slot and aseries of 0.188 inch diameter apertures. The part being elongated with arelatively thin cross section vibratory processing is selected.

The media used is preformed triangular bodies of aluminum oxide inch oneach side and "E1 inch thick. This media body is sufliciently small topass through the half 4 inch aperture and the slot while being excludedfrom the 0.188 inch apertures. The vibratory tub is loaded with media tothe operating level and water added in sufiicient quantity to maintainthe media and part surfaces moist. Thereafter a grinding compound formedof finely ground aluminum oxide and low foaming detergent is added.Following mixing of the media the parts are added, subjected to a fivehour vibratory cycle and rinsed after processing.

The part as received following electroplating of the silicon carbide andnickel coating has a surface finish with a mean value of 100AA, fallingwithin the range of 110AA, while the required final finish is 32AA.Following the vibratory process as defined above, a surface finish inthe range of 16-25AA is attained.

While the invention has been particularly described with reference topreferred embodiments thereof, it will be understood that the foregoingand other changes in the form and details may be made therein withoutdepart ing from the spirit and scope of the invention.

What is claimed is:

1. A method of treating the surface of an article having particles ofhard, abrasion resistant material embedded in a matrix of metal toremove irregularities and establish a smooth surface finish withoutcausing significant removal of material comprising:

establishing relatively sliding contact between said article and anaggressive preformed ceramic media in the presence of a liquidcontaining a wetting agent.

2. The method of claim 1 wherein said sliding contact is induced bytumbling said article in the presence of said ceramic media and saidliquid is water present in a quantity to bring the level of said waterto the level of said media.

3. The method of claim 2 wherein said media comprises preformed bodiesof aluminum oxide.

4. The method of claim 2 wherein said water has therein a light grindingcompound comprising a finely ground hard, wear resistant material and adetergent comprising said wetting agent.

5. The method of claim 3 wherein the article surface to be treated is anelectroplated nickel matrix having discrete particles of silicon carbidehomogeneously dispersed therein and the performed media bodies are of asize and configuration to prevent lodging thereof in article aperturesor recesses.

6. The method of claim 1 wherein said article and ceramic media are heldwithin a container and said sliding contact is induced by imparting avibratory motion to said container holding said article and said ceramicmedia.

7. The method of claim 6 wherein said liquid is water present insufficient quantity to maintain a liquid film on article and mediasurfaces throughout the vibratory operation.

8. The method of claim 7 wherein said liquid has therein a low foaminggrinding compound comprising a low foaming detergent that functions assaid wetting agent and finely ground hard, wear resistant material.

9. The method of claim 7 wherein the article surface to be treated is anelectroplated nickel matrix having discrete particles of silicon carbidehomogeneously dispersed therein and the preformed media bodies are of asize and configuration to prevent lodging thereof in article aperturesor recesses.

References Cited UNITED STATES PATENTS 6/1913 Uebersax 51-313 3/1966Bishop 51313 US. Cl. X.R. 51-317

